Microstructure and magnetic properties of strip-cast grain-oriented 4.5%Si steel under isochronal and isothermal secondary annealing

Strip-cast grain-oriented 4.5% Si steel was produced by short-term isochronal secondary annealing (15 min) and isothermal annealing (1000 °C) under hydrogen atmosphere. The relationship between the evolution of grain structure and magnetic properties was elucidated. It was observed that during isochronal annealing, abnormal grain growth occurred followed by normal grain growth with the increase of annealing temperature. Additionally, decreasing the primary annealing temperature accelerated the isochronal annealing kinetics, and near complete abnormal grain growth with optimal magnetic properties was obtained at lower temperature. Furthermore, during isothermal annealing, abnormal grain growth successfully occurred and magnetic properties were continuously improved with the increase of annealing time. The optimal magnetic properties were superior to those of isochronal annealing because of sharper secondary Goss texture and reduced retention of second-phase particles. The grain-oriented 4.5%Si steel in the present study indicated superior properties and better workability than the previously reported non-oriented 6.5%Si steel. Thus, grain-oriented 4.5%Si steel produced by short-term secondary annealing can potentially replace non-oriented 6.5%Si steel.